Mechanical tensioner strut with uni-directional friction damping

ABSTRACT

A strut including a housing, a plunger within a space in the housing and including a tapered outer circumferential surface, a primary spring engaged with the housing, a wedge element within the space and including a tapered inner circumferential surface engageable with the outer circumferential surface, and a secondary spring engaged with the wedge element and the plunger to urge the plunger in an axial direction. The primary spring urges the plunger in the axial direction with a first force. In a fully extended mode, the plunger is maximally displaced in the axial direction. In a contracted mode, the plunger is displaced in an opposite axial direction in response to application of a second force, sufficiently greater than the first force, on the plunger in the opposite axial direction. When the second force is sufficiently decreased, the plunger displaces with respect to the housing in the axial direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/044,922, filed Oct. 3, 2013, entitled, “MECHANICAL TENSIONER STRUTWITH UNI-DIRECTIONAL FRICTION DAMPING”, which application claims thebenefit under 35 U.S.C. §119(e) of U.S. Provisional Application No.61/711,781, filed Oct. 10, 2012, which applications are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to a mechanical tensioner strut with adisplaceable wedge and secondary spring to enable increased dampening.

BACKGROUND

Mechanical tensioner struts are used to absorb or dampen force appliedto the strut in a first direction by displacing a first component, towhich the force is applied, in the first direction with respect to afixed component of the strut. For example, struts are used to modulateforce and vibration associated with operation of chain systems. A springfor the strut opposes the displacement of the first component in thefirst direction and the degree of displacement of the first component isa function of the relative magnitude of the applied force with respectto the spring force. Upon release or reduction of the force, the springdisplaces the first component in a second direction, opposite the firstdirection, with respect to the fixed component. It is desirable toeliminate or minimize dampening of the first component in the seconddirection. That is, ideally, the dampening of the strut isuni-directional only in the first direction.

To maximize dampening in the first direction, frictional forcesgenerated by contact of the first component with other components of thestrut are maximized. However, maximizing these frictional forcesmaximizes forces which lock the first component in a contracted position(displaced a maximum distance in the first direction). If these forcesare too great, the spring is unable to displace the first component inthe second direction when the force in the first direction is reduced orremoved. Further, even if the spring is able to displace the firstcomponent in the second direction when the force in the first directionis reduced or removed, the frictional forces may still be present duringthe displacement in the second direction, resulting in undesirabledampening in the second direction.

U.S. Pat. Nos. 6,702,266; 6,612,408; 5,951,423; and 4,606,442 as well asU.S. Patent Application Publication No. 2002/0025869 disclose the use ofcomplementarily angled and mating respective surfaces for componentsengaged during operations to dampen a force applied in a firstdirection. Decreasing the complementary angles increases desireddampening. However, to prevent the surfaces from locking together (dueto frictional and compressive forces), which would prevent desireddisplacement in a second opposite direction when the force is reduced orremoved, or would result in undesirable dampening in the seconddirection, the angles must be kept relatively large. That is, if theangles are too small, the engagement of the respective surfaces resultsin such a large frictional/compressive force holding the respectivesurfaces in contact that the surfaces remain locked or at leastpartially engaged when the force is reduced or removed. Thus, the rangeof operation of the respective devices is undesirably restricted and/orundesired dampening in the second direction occurs.

SUMMARY

According to aspects illustrated herein, there is provided a mechanicaltensioner strut, including: a housing including a first internal space;a plunger at least partially disposed within the first internal spaceand including a first outer circumferential surface tapering in a firstaxial direction; a primary spring including a first end and a second endengaged with the housing; a wedge element disposed within the firstinternal space and including at least one first inner circumferentialsurface tapering in a second axial direction, opposite the first axialdirection, and directly engageable with the first outer circumferentialsurface; and a secondary spring directly engaged with the wedge elementand at least a portion of the plunger to urge the at least a portion ofthe plunger in the second axial direction. The primary spring urges theplunger in the second axial direction, with respect to the housing, witha first force. In a fully extended mode, the plunger is displaced amaximum distance in the second axial direction with respect to thehousing. In a contracted mode, the plunger is displaced a seconddistance, with respect to the housing in the first axial direction, inresponse to application of a second force, greater by a first amountthan the first force, on the plunger in the first axial direction. Whenthe second force is decreased by a second amount, the plunger isconfigured to displace with respect to the housing in the second axialdirection.

According to aspects illustrated herein, there is provided a mechanicaltensioner strut, including a housing including a first internal space; aplunger including a nose and a slide. The nose is at least partiallydisposed within the first internal space and includes a second internalspace and a first outer circumferential surface tapering in a firstaxial direction. The slide is at least partially disposed within thefirst and second internal spaces. The strut includes a spring and awedge element. The spring includes a first end directly engaged with thehousing and a second end directly engaged with the slide; and urges,with a first force, the slide in a second axial direction, opposite thefirst axial direction, with respect to the housing. The wedge element isdisposed within the first internal space, is directly engaged with theslide, and includes at least one first inner circumferential surfacetapering in the second axial direction and directly engageable with thefirst outer circumferential surface. In a fully extended mode, the noseis displaced a maximum distance in the second axial direction withrespect to the housing. In a contracted mode, the nose is displaced inthe first axial direction with respect to the housing, in response toapplication of a second force, greater by a first amount than the firstforce, on the nose in the first axial direction. When the second forceis decreased by a second amount, the slide is configured to displacewith respect to the housing in the second axial direction.

According to aspects illustrated herein, there is provided a method ofdampening movement using a mechanical tensioner strut including: ahousing including a first internal space; a plunger at least partiallydisposed within the first internal space and including a first outercircumferential surface tapering in a first axial direction; a primaryspring including a first end and a second end engaged with the housing;a wedge element disposed within the first internal space and includingat least one first inner circumferential surface tapering in a secondaxial direction, opposite the first axial direction, and directlyengageable with the first outer circumferential surface; and a secondaryspring directly engaged with the wedge element and at least a portion ofthe plunger. The method includes: applying, using the primary spring, afirst force to the plunger; displacing the plunger in the second axialdirection with respect to the housing; urging the at least a portion ofthe plunger in the second axial direction, with respect to the housing,with the secondary spring; displacing, using the primary spring, theplunger a maximum distance in the second axial direction with respect tothe housing; applying a second force, greater by a first amount than thefirst force, to the plunger in the first axial direction; displacing theplunger in the first axial direction with respect to the housing;decreasing the second force by a second amount; and displacing theplunger with respect to the housing in the second axial direction.

According to aspects illustrated herein, there is provided a method ofdampening movement using a mechanical tensioner strut including: ahousing including a first internal space; a plunger including a nose atleast partially disposed within the first internal space and including asecond internal space and a first outer circumferential surface taperingin a first axial direction, and a slide at least partially disposedwithin the first and second internal spaces; a spring including a firstend directly engaged with the housing and a second end directly engagedwith the slide; and a wedge element disposed within the first internalspace, directly engaged with the slide, and including at least one firstinner circumferential surface tapering in the second axial direction anddirectly engageable with the first outer circumferential surface. Themethod includes: applying, using the primary spring, a first force tothe slide; displacing the slide and the nose in a second axialdirection, opposite the first axial direction, with respect to thehousing; applying a second force, greater by a first amount than thefirst force, on the nose in the first axial direction; displacing theslide and the nose in the first axial direction with respect to thehousing; decreasing the second force by a second amount; and displacingthe slide and the nose with respect to the housing in the second axialdirection.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments are disclosed, by way of example only, withreference to the accompanying schematic drawings in which correspondingreference symbols indicate corresponding parts, in which:

FIG. 1A is a perspective view of a cylindrical coordinate systemdemonstrating spatial terminology used in the present application;

FIG. 1B is a perspective view of an object in the cylindrical coordinatesystem of FIG. 1A demonstrating spatial terminology used in the presentapplication; and,

FIG. 2 is a perspective view of a mechanical tensioner strut withsecondary spring;

FIG. 3 is a cross-sectional view of the mechanical tensioner strut shownin FIG. 2 in a fully extended mode;

FIG. 3A is a detail of area 3A of FIG. 3;

FIG. 4 is a cross-sectional view of the mechanical tensioner strut shownin FIG. 3 in the contracted mode;

FIG. 4A is a detail of area 4A of FIG. 4;

FIG. 5 is a perspective view of the wedge element shown in FIG. 2;

FIG. 6 is a cross-sectional view of the mechanical tensioner strut shownin FIG. 2 with a slide and in a fully extended mode;

FIG. 7 is a cross-sectional view of the mechanical tensioner strut shownin FIG. 6 in a contracted mode;

FIG. 8 is a perspective view of the mechanical tensioner shown in FIG. 2in a fully extended mode; and,

FIG. 9 is a perspective view of the mechanical tensioner strut shown inFIG. 8 in a contracted mode.

DETAILED DESCRIPTION

At the outset, it should be appreciated that like drawing numbers ondifferent drawing views identify identical, or functionally similar,structural elements of the disclosure. It is to be understood that thedisclosure as claimed is not limited to the disclosed aspects.

Furthermore, it is understood that this disclosure is not limited to theparticular methodology, materials and modifications described and assuch may, of course, vary. It is also understood that the terminologyused herein is for the purpose of describing particular aspects only,and is not intended to limit the scope of the present disclosure.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which this disclosure belongs. It should be understood thatany methods, devices or materials similar or equivalent to thosedescribed herein can be used in the practice or testing of thedisclosure.

FIG. 1A is a perspective view of cylindrical coordinate system 80demonstrating spatial terminology used in the present application. Thepresent invention is at least partially described within the context ofa cylindrical coordinate system. System 80 has a longitudinal axis 81,used as the reference for the directional and spatial terms that follow.The adjectives “axial,” “radial,” and “circumferential” are with respectto an orientation parallel to axis 81, radius 82 (which is orthogonal toaxis 81), and circumference 83, respectively. The adjectives “axial,”“radial” and “circumferential” also are regarding orientation parallelto respective planes. To clarify the disposition of the various planes,objects 84, 85, and 86 are used. Surface 87 of object 84 forms an axialplane. That is, axis 81 forms a line along the surface. Surface 88 ofobject 85 forms a radial plane. That is, radius 82 forms a line alongthe surface. Surface 89 of object 86 forms a circumferential plane. Thatis, circumference 83 forms a line along the surface. As a furtherexample, axial movement or disposition is parallel to axis 81, radialmovement or disposition is parallel to radius 82, and circumferentialmovement or disposition is parallel to circumference 83. Rotation iswith respect to axis 81.

The adverbs “axially,” “radially,” and “circumferentially” are withrespect to an orientation parallel to axis 81, radius 82, orcircumference 83, respectively. The adverbs “axially,” “radially,” and“circumferentially” also are regarding orientation parallel torespective planes.

FIG. 1B is a perspective view of object 90 in cylindrical coordinatesystem 80 of FIG. 1A demonstrating spatial terminology used in thepresent application. Cylindrical object 90 is representative of acylindrical object in a cylindrical coordinate system and is notintended to limit the present invention in any manner. Object 90includes axial surface 91, radial surface 92, and circumferentialsurface 93. Surface 91 is part of an axial plane, surface 92 is part ofa radial plane, and surface 93 is a circumferential surface.

FIG. 2 is a perspective view of mechanical tensioner strut 100/200/300.

FIG. 3 is a cross-sectional view of mechanical tensioner strut 100 shownin FIG. 2 in a fully extended mode.

FIG. 3A is a detail of area 3A of FIG. 3.

FIG. 4 is a cross-sectional view of mechanical tensioner strut 100 shownin FIG. 3 in a contracted mode

FIG. 4A is a detail of area 4A of FIG. 4.

FIG. 5 is a perspective view of the wedge element shown in FIG. 2. Thefollowing should be viewed in light of FIGS. 2 through 5. Strut 100includes housing 102, plunger 104, wedge element 106, primary spring108, and secondary spring 110. In an example embodiment, the secondaryspring is located radially outward of the primary spring. Housing 102includes internal space 112. The plunger is at least partially disposedwithin space 112 and is axially displaceable with respect to thehousing. The plunger includes outer circumferential surface OCS1tapering in axial direction AD1. The wedge element is disposed withinthe space 112 and includes at least one inner circumferential surfaceICS1 tapering in axial direction AD2, opposite AD1. Surface OCS1 isdirectly engaged with ICS1 as further described below. By “tapering” inan axial direction, we mean that a radial thickness of a componentdecreases in the direction of the taper. For example, radial thicknessRT of the wedge element is greatest at end E3 and smallest at end E4.

Primary spring 108 includes end E1 directly engaged with the wedgeelement and end E2 directly engaged with the housing. In an exampleembodiment, spring 112 is in direct contact with one or both of thewedge element and the housing. The primary spring urges the plunger inaxial direction AD2, with respect to the housing, with force F1. Thesecondary spring is directly engaged with at least a portion of theplunger and the wedge element to urge the portion of the plunger indirection AD2 with respect to the wedge element. The primary andsecondary springs can be any spring or resilient element known in theart, for example including but not limited to a coil spring, a wavewasher, or a Bellville spring, possessing the characteristics necessaryto perform the functions described above and below. For instance, therespective spring rates of the primary and secondary springs can beselected according to application requirements.

In a fully extended mode, for example as shown in FIG. 3, the plunger isdisplaced maximum distance MD in direction AD2 with respect to thehousing. In a contracted mode, for example as shown in FIG. 4, theplunger is displaced in direction AD1 with respect to the housing, inresponse to application of force F2 on the plunger in direction AD1. F2is at least greater than force F1 by an amount of friction force FF1,generated by contact between at least one outer circumferential surfaceOCS2 of the wedge element and inner circumferential surface ICS2 of thehousing, opposing the movement of the plunger in axial direction AD1.When F2 is decreased by a sufficient amount, the plunger is configuredto displace with respect to the housing in direction AD2. In a fullycontracted mode, spring 104 is fully compressed and the plunger isdisplaced to a maximum extent in direction AD1 with respect to thehousing. In actual operation, strut 100 can at various times be inintermediate states between a fully extended and a fully contractedmode.

When the plunger is displaced in direction AD1, friction force FF1 isgenerated as noted above. Also, during displacement of the plunger indirection AD1, ICS1 contacts OCS1 to urge OCS2 radially outward toincrease FF1. For example, as OCS1 slides along ICS1 in direction AD1,OCS1 applies radially outward force RF1 to ICS1, which in turn urgesOCS2 against ICS2 with radially outward force RF2 to increase FF1. Thewedge element displaces in direction AD1 against F1 and FF2,advantageously increasing the dampening in direction AD1. In an exampleembodiment, in the absence of RF2, FF1 has a nominal value as describedbelow.

As noted above, in the contracted mode, radial forces RF1 and RF2 andfriction forces FF1 and FF2 are generated, or are present. To enableun-dampened displacement of the plunger in direction AD2 (the transitionfrom the contract mode to the extended mode when force F2 is reduced),FF1 must be reduced to a sufficiently small magnitude. To accomplishthis, the plunger must displace in direction AD2 with respect to thewedge element to reduce RF1 and RF2. To enable the displacement of theplunger in direction AD2, force FF2 must be overcome. Advantageously,the secondary spring urges the plunger in direction AD2 with force F3which, in combination with force FF1, is sufficient to displace theplunger in direction AD2 with respect to the wedge element. That is, FF2is less than the sum of FF1 and F3. In general, to optimize damping indirection AD1, FF2 is at least equal to FF1. In this case, without forceF3, the plunger is not displaceable in direction AD2 with respect to thewedge element.

In an example embodiment, wedge element 106 includes circumferential gap114. In a free/un-installed state, the wedge element has an outsidediameter D1 less than diameter D2 of space 112. Thus, when the wedgeelement is installed in space 112, the wedge element radially contractssuch that gap 114 is reduced and diameter D1 is substantially equal toD2. The reduction of gap 114 and D1 results in OCS2 exerting nominalforce FF1 mentioned above in the absence of RF2. In general, nominalforce FF1 is adequate to maintain an axial position of the wedge elementin the absence of axial forces on the wedge element, while minimizingresistance to axial displacement of the wedge element in direction AD2.

In an example embodiment, circumferential surface OCS1 or ICS1 is atacute angle AA1 of between 5 and 20 degrees with respect to longitudinalaxis LX for strut 100 and OCS1 and ICS1 are substantially parallel.Decreasing angle AA1 desirably increases dampening in direction AD1 andas noted above, force F3 provided by the secondary spring enables theangle to be decreased.

In an example embodiment, coating 116 is applied to one or both ofsurfaces OCS1 or ICS1 to reduce the magnitude of FF2, which furtherenables a reduction of AA1 or F3. Any coating known in the art can beused.

FIG. 6 is a cross-sectional view of mechanical tensioner strut 200 shownin FIG. 2 with slide 202 and in an extended mode.

FIG. 7 is a cross-sectional view of mechanical tensioner strut 200 shownin FIG. 6 in a contracted mode. The following should be viewed in lightof FIGS. 2 through 7. Strut 200 includes housing 102, plunger 104, wedgeelement 106, primary spring 204, and secondary spring 110. Housing 102includes internal space 112. Plunger 104 includes slide 202 and nose206. The nose is at least partially disposed within internal space 112and includes internal space 208 and distal end E5 arranged to receiveF2. The slide is at least partially disposed within spaces 112 and 208and includes internal space 210 partially enclosing the primary spring,end E6 directly engaged with end E1 of the primary spring and end E7directly engaged with the wedge element. End E2 of the primary spring isdirectly engaged with the housing.

In the fully extended mode, for example, as shown in FIG. 6, the noseand slide are each displaced maximum distances MD2 and MD3,respectively, in direction AD2 with respect to the housing. In acontracted mode, for example as shown in FIG. 7, the nose and slide aredisplaced in direction AD1 with respect to the housing, in response toapplication of force F2 on the plunger in direction AD1. F2 is at leastgreater than force F1 by amount FF1 described above. When F2 isdecreased by a sufficient amount, the nose and slide are configured todisplace with respect to the housing in direction AD2. In a fullycontracted mode, spring 204 is fully compressed and the nose and slideare displaced to a maximum extent in direction AD1 with respect to thehousing. In actual operation, strut 200 can at various times be inintermediate states between a fully extended and a fully contractedmode.

The nose includes outer circumferential surface OCS1 tapering in axialdirection AD1. The wedge element is disposed within space 112 andincludes at least one inner circumferential surface ICS1 tapering inaxial direction AD2, opposite AD1. Surface OCS1 is directly engaged withICS1 as further described below.

The primary spring urges the slide, and subsequently, the wedge elementand nose, in axial direction AD2, with respect to the housing, withforce F1. The secondary spring is directly engaged with the nose and thewedge element to urge the nose in direction AD2 with respect to thewedge element. The primary and secondary springs can be any spring orresilient element known in the art, for example including but notlimited to a coil spring, a wave washer, or a Bellville spring,possessing the characteristics necessary to perform the functionsdescribed above and below. For instance, the respective spring rates ofthe primary and secondary springs can be selected according toapplication requirements.

The fundamental operation of strut 200 is similar to the operation ofstrut 100 with the exception that in strut 100 the primary springdirectly engages the wedge element, while in strut 200, the primaryspring directly engage the slide, which in turn directly engages thewedge element.

FIGS. 3A and 4A are applicable to the following discussion with theunderstanding that force from the primary spring in direction AD2 isapplied to the wedge element indirectly by slide 202. When the nose isdisplaced in direction AD1, friction force FF1 is generated. Also,during displacement of the plunger in direction AD1, ICS1 contacts OCS1to urge OCS2 radially outward to increase FF1. For example, as OCS1slides along ICS1 in direction AD1, OCS1 applies radially outward forceRF1 to ICS1, which in turn urges OCS2 against ICS2 with radially outwardforce RF2 to increase FF1. Note that in the absence of RF1, FF1 has anominal value as described above. As the wedge element displaces indirection AD1, the wedge element pushes the slide element in directionAD1 against F1 and FF1, advantageously increasing the dampening indirection AD1.

As noted above, in the contracted mode, radial forces RF1 and RF2 andfriction forces FF1 and FF2 are generated, or are present. To enableun-dampened displacement of the plunger in direction AD2 (the transitionfrom the contract mode to the extended mode when force F2 is reduced),FF1 must be reduced to a sufficiently small magnitude. To accomplishthis, the nose must displace in direction AD2 with respect to the wedgeelement to reduce RF1 and RF2. However, to enable the displacement ofthe nose in direction AD2, force FF2 must be overcome.

Advantageously, the secondary spring urges the nose in direction AD2with force F3 which, in combination with force FF1, is sufficient todisplace the nose in direction AD2 with respect to the wedge element.That is, FF2 is less than the sum of FF1 and F3. In general, to optimizedamping in direction AD1, FF2 is at least equal to FF1. Thus, withoutforce F3, the nose is not displaceable in direction AD2 with respect tothe wedge element. Once FF2 is reduced, the slide displaces in directionAD2, subsequently displacing the wedge element and nose.

FIG. 8 is a perspective view of the mechanical tensioner strut shown inFIG. 2 in an extended mode.

FIG. 9 is a perspective view of the mechanical tensioner strut shown inFIG. 8 in a contracted mode. The following should be viewed in light ofFIGS. 8 and 9. Strut 300 includes housing 102, plunger 104, wedgeelement 106, and spring 204. Housing 102 includes internal space 112.Plunger 104 includes slide 202 and nose 206. The nose is at leastpartially disposed within internal space 112 and includes internal space208 and distal end E5 arranged to receive F2. The slide is at leastpartially disposed within spaces 112 and 208 and includes internal space210 partially enclosing the primary spring, end E6 directly engaged withend E1 of the primary spring and end E7 directly engaged with the wedgeelement. End E2 of the primary spring is directly engaged with thehousing.

In the fully extended mode, for example, as shown in FIG. 8, the noseand slide are each displaced maximum distances MD2 and MD3,respectively, in direction AD2 with respect to the housing. In acontracted mode, for example as shown in FIG. 9, the nose and slide aredisplaced in direction AD1 with respect to the housing, in response toapplication of force F2 on the plunger in direction AD1. F2 is at leastgreater than force F1 by amount FF1. When F2 is decreased by asufficient amount, the nose and slide are configured to displace withrespect to the housing in direction AD2. In a fully contracted mode,spring 204 is fully compressed and the nose and slide are displaced to amaximum extent in direction AD1 with respect to the housing. In actualoperation, strut 300 can at various times be in intermediate statesbetween a fully extended and a fully contracted mode.

The nose includes outer circumferential surface OCS1 tapering in axialdirection AD1. The wedge element is disposed within space 112 andincludes at least one inner circumferential surface ICS1 tapering inaxial direction AD2, opposite AD1. Surface OCS1 is directly engaged withICS1.

The spring urges the slide, and subsequently, the wedge element andnose, in axial direction AD2, with respect to the housing, with forceF1. The spring can be any spring or resilient element known in the art,for example including but not limited to a coil spring, a wave washer,or a Bellville spring, possessing the characteristics necessary toperform the functions described above and below. For instance, thespring rates of the spring can be selected according to applicationrequirements.

Regarding struts 100 and 200, as noted above; to maximize desireddampening in direction AD1, frictional force FF1 generated by contact ofthe wedge element with the housing should be maximized. Advantageously,angle AA1 is minimized to increase RF1 and RF2, which subsequentlyincreases FF1. However, as noted above, increasing frictional forces cancause the strut to jam in the contracted mode or can result inundesirable dampening in direction AD2 (FF1 and FF2 are not adequatelyreduced). Advantageously, the secondary spring offsets the desirableincrease in friction forces by providing a means to overcome theincrease in force FF2 between the wedge and the plunger. That is, theforce from the secondary spring advantageously enables the plunger todisplace with respect to the wedge element in direction AD2, desirablyreducing RF1 and RF2 and subsequently, FF1.

Regarding struts 200 and 300, the use of a nose/slide configurationadvantageously enables a longer length L1 for spring 204 than ispossible for spring 104 in strut 100. Increasing length L1 results in adesirable increase in spring force. The increase in spring forceadvantageously increases the desired dampening in direction AD2.

Struts 200 and 300 provide the following advantages:

-   -   1. The overall length L2 of strut 200 or 300 can be less than        overall length L3 of strut 100 for a given stroke requirement.        The length of the primary spring is proportional to the stroke        requirement. In strut 100, length L4 between end E8 of the        housing and the wedge element is available for spring 108.        However, in strut 200 or 300, length L1 available for spring        204, between end E8 and end E6 of the slide is considerably        greater. Therefore, for a same size housing and nose/plunger, L1        is longer than L4. Thus, for strut 100 to include spring 108        comparable to spring 204 in performance, length L4, and hence        length L3, would need to be increased.    -   2. Provide reduced variability in the return spring force over        the tensioner stroke range, thereby reducing the average        tensioner force. This is due to the fact that for a same stroke        performance, length L4 is less than length L1 and the spring        rate for 204 is less than the spring rate for 108.    -   3. Because length L1 is less than length L4 for a same stroke        performance, the likelihood of spring 204 fully compressing is        reduced, which in turn reduces possible damage to spring 204.    -   4. Because length L1 is less than length L4 for a same stroke        performance, spring 204 is generally compressed to a lesser        degree than spring 108 over the respective operating ranges of        the struts, which reduces fatigue and increases primary spring        life.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Variouspresently unforeseen or unanticipated alternatives, modifications,variations, or improvements therein may be subsequently made by thoseskilled in the art which are also intended to be encompassed by thefollowing claims.

What is claimed is:
 1. A mechanical tensioner strut, comprising: ahousing including a first internal space; a plunger at least partiallydisposed within the first internal space and including a first outercircumferential surface tapering in a first axial direction; a primaryspring including a first end and a second end engaged with the housing;a wedge element disposed within the first internal space and includingat least one first inner circumferential surface tapering in a secondaxial direction, opposite the first axial direction, and directlyengageable with the first outer circumferential surface; and, asecondary spring directly engaged with the wedge element and at least aportion of the plunger to urge the at least a portion of the plunger inthe second axial direction, wherein: the secondary spring is locatedradially outward of the primary spring; the primary spring extends pastthe secondary spring in the first and second axial directions; theprimary spring urges the plunger in the second axial direction, withrespect to the housing, with a first force; in a fully extended mode,the plunger is displaced a maximum distance in the second axialdirection with respect to the housing; in a contracted mode, the plungeris displaced a second distance, with respect to the housing, in thefirst axial direction in response to application of a second force,greater by a first amount than the first force, on the plunger in thefirst axial direction; and, when the second force is decreased by asecond amount, the plunger is configured to displace with respect to thehousing in the second axial direction.
 2. The mechanical tensioner strutof claim 1, wherein the secondary spring is located radially outward ofthe primary spring.
 3. The mechanical tensioner strut of claim 1,wherein: the plunger includes: a nose: at least partially disposedwithin the first internal space; and, including the first outercircumferential surface, a distal end arranged to receive the secondforce, and a second internal space; and a slide at least partiallydisposed within the first and second internal spaces and including: athird internal space partially enclosing the primary spring; a first enddirectly engaged with the primary spring; and, a second end directlyengaged with the wedge element, wherein: in the fully extended mode, thenose and slide are each displaced respective third maximum distance inthe second axial direction with respect to the housing; and, in thecontracted mode, the nose and slide are each displaced respective fourthmaximum distances, with respect to the housing in the first axialdirection.
 4. A method of dampening movement using a mechanicaltensioner strut including: a housing including a first internal space; aplunger at least partially disposed within the first internal space andincluding a first outer circumferential surface tapering in a firstaxial direction; a primary spring including a first end and a second endengaged with the housing; a wedge element disposed within the firstinternal space and including at least one first inner circumferentialsurface tapering in a second axial direction, opposite the first axialdirection, and directly engageable with the first outer circumferentialsurface; and a secondary spring directly, located radially outward ofthe primary spring, engaged with the wedge element and at least aportion of the plunger, the method comprising: applying, using theprimary spring, a first force to the plunger; displacing the plunger inthe second axial direction with respect to the housing; urging the atleast a portion of the plunger in the second axial direction, withrespect to the housing, with the secondary spring; applying a secondforce, greater by a first amount than the first force, to the plunger inthe first axial direction; displacing the plunger in the first axialdirection with respect to the housing; decreasing the second force by asecond amount; displacing the plunger with respect to the housing in thesecond axial direction; and, maintaining first and second axial ends ofthe primary spring past the secondary spring in the first and secondaxial directions, respectively.
 5. The method of claim 4, whereindisplacing the plunger in the first axial direction with respect to thehousing includes: generating a first friction force, opposingdisplacement of the plunger and the wedge element in the first axialdirection, between a second inner circumferential surface of the housingand at least one second outer circumferential surface of the wedgeelement; and, displacing the wedge element in the first axial directionwith respect to the housing.
 6. The method of claim 5, furthercomprising: contacting the first outer circumferential surface with theat least one first inner circumferential surface during displacement ofthe plunger in the first axial direction; and, urging the at least onesecond outer circumferential surface radially outward to increase thefirst friction force.
 7. The method of claim 4, further comprising, whenthe plunger is displaced in the second axial direction: generating afirst friction force between the first outer circumferential surface andthe at least one first inner circumferential surface; generating asecond frictional force between at least one second outercircumferential surface of the wedge element and a second innercircumferential surface of the housing; and, urging, with the secondaryspring, the at least a portion of the plunger in the second axialdirection with a third force, wherein the first frictional force is lessthan the sum of the second frictional force and the third force.
 8. Themethod of claim 7, further comprising: displacing, using the secondaryspring, the at least a portion of the plunger in the second axialcondition with respect to the wedge element; and, reducing a magnitudeof the second frictional force.
 9. The method of claim 7, furthercomprising: contacting the first outer circumferential surface with theat least one first inner circumferential surface; urging the at leastone second outer circumferential surface against the second innercircumferential surface with a radial force; decreasing the second forceby the second amount; and, displacing the at least a portion of theplunger in the second axial condition to reduce a magnitude of theradial force.
 10. The method of claim 4, wherein: the secondary springis located radially outward of the primary spring; or, the secondaryspring is at least partially aligned with the primary spring in thefirst or second axial direction.
 11. The method of claim 4, wherein: theplunger includes: a nose: at least partially disposed within the firstinternal space; and, including the first outer circumferential surface,a distal end arranged to receive the second force, and a second internalspace; and a slide at least partially disposed within the first andsecond internal spaces and including: a third internal space partiallyenclosing the primary spring; a first end directly engaged with theprimary spring; and, a second end directly engaged with the wedgeelement; displacing the plunger in the second axial direction withrespect to the housing includes displacing the nose and the slide in thesecond axial direction with respect to the housing; and, displacing theplunger in the first axial direction with respect to the housingincludes displacing the nose and the slide in the first axial directionwith respect to the housing.
 12. The method of claim 4, wherein thefirst outer circumferential surface or the at least one first innercircumferential surface is at a first angle of between 5 and 20 degreeswith respect to a longitudinal axis for the mechanical tensioner strut.